mpi4: support MPI_INFO_ENV before MPI_Init

[hzhou]

link:

• Create MPI_INFO_ENV before MPI_INIT mpi-forum/mpi-issues#143

[raffenet]

One piece of background for this ticket: Sessions introduces the ability to manipulate Info objects before init (and after finalize) of MPI. MPI_T also will take advantage of this capability.

Because of the requirement to be available outside of initialization, all related Info manipulation functions must always be thread-safe.

[shintaro-iwasaki]

If it is the case, the problem would be using atomic operations for "thread-safety" before MPI_Init().

[hzhou]

\begin{mpi-binding}
    function_name("MPI_Info_create_env")

    parameter(
        "argc",
        "ARGUMENT_COUNT",
        direction="inout",
        pointer=False,
        suppress="lis_parameter f08_parameter f90_parameter",
    )
    parameter(
        "argv",
        "ARGUMENT_LIST",
        length="argc",
        pointer=False,
        direction="inout",
        suppress="lis_parameter f08_parameter f90_parameter",
    )

    parameter("info", "INFO", direction="out", desc="info object")
\end{mpi-binding}

This routine produces an output object \mpiarg{info} with the same construction as
\const{MPI\_INFO\_ENV} as created during \mpifunc{MPI\_INIT} or \mpifunc{MPI\_INIT\_THREAD} when the
same arguments are used.
This construction is described in Section~\ref{sec:inquiry-startup};
however, this function can be called when not using the \wpm{}, e.g., when using the \spm{}.
This object is not a direct
copy or alias of the \const{MPI\_INFO\_ENV} object and could contain different values based on the
input arguments and other sources.  Multiple calls to this procedure that are given the same input
arguments will produce \mpiarg{info} objects consistent with the definition of
\const{MPI\_INFO\_ENV}.  The version for ISO C accepts the \mpiarg{argc} and \mpiarg{argv} that are
provided by the arguments to \code{main} or \code{0} for \mpiarg{argc} and \code{NULL} for
\mpiarg{argv}.  The user is responsible for freeing the \mpiarg{info} object via
\mpifunc{MPI\_INFO\_FREE}.  This procedure is local.

This procedure must always be thread-safe, as defined in Section~\ref{sec:dynamic:threads}.  It is
one of the few routines that may be called before \MPI/ is initialized or after \MPI/ is finalized.

\begin{users}

    In some circumstances (e.g., when passing \code{0} to \mpiarg{argc} and \code{NULL} to
    \mpiarg{argv} in C or in Fortran where such arguments do not exist), the \mpiarg{info} object
    may not be populated or may be populated incompletely because this procedure is local and the
    implementation may not be able to determine the correct values. Note that this could result in
    different values in the resulting \mpiarg{info} object at different \MPI/ processes.

\end{users}